1. Field of the Invention
The present invention relates to metal interconnect structures and, more particularly, to a metal interconnect structure with a side wall spacer that protects an anti-reflective coating (ARC) layer and a bond pad from corrosion.
2. Description of the Related Art
One of the final processing steps in the fabrication of an integrated circuit is the formation of bond pads, which are commonly formed around the periphery of the top surface of the integrated circuit. Bond pads, which are part of the metal interconnect structure, provide a location to which external electrical connections are made to the integrated circuit.
FIG. 1 shows a cross-sectional view that illustrates a portion of a conventional metal interconnect structure 100. As shown in FIG. 1, the metal interconnect structure 100 includes a non-conductive layer 110, a conductive via 112 that extends through the non-conductive layer 110, and a conductive bond pad 114 that touches the top surface of the non-conductive layer 110 and the conductive via 112. The bond pad 114 is commonly implemented with aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper.
As further shown in FIG. 1, the metal interconnect structure 100 also includes an anti-reflective coating (ARC) layer 116 that touches the top surface of the bond pad 114, and a passivation layer 118 that touches the top surface of the non-conductive layer 110 and the top surface of the ARC layer 116. The ARC layer 116 is commonly implemented with titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW), or tantalum nitride (TaN), while the passivation layer 118 is commonly implemented with an oxide layer 118A and an overlying nitride layer 118B.
In addition, an opening 120 in the passivation layer 118 and the ARC layer 116 exposes the top surface of the bond pad 114. The bond pad 114, which is electrically connected to transistors and other devices that make up the integrated circuit, is electrically connected to the outside world by way of a bonding wire or a solder ball.
After the fabrication of the integrated circuit has been completed, the integrated circuit is subjected to reliability testing under high humidity, high temperature, and high voltage bias conditions. One of the problems encountered during the reliability testing is that moisture can react with the titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW), or tantalum nitride (TaN) of the ARC layer 116 that is exposed by the opening 120.
This reaction, in turn, forms a corrosive by-product that can oxidize the bond pad 114, thereby significantly increasing the resistance of the bond pad 114, or electrically isolating the bond pad 114 from the conductive via 112. The corrosive by-product can also form cracks in the passivation layer 118, and electrically short the bond pad 114 to other conductive structures.
Thus, there is a need for a method of testing integrated circuits under high humidity, high temperature, and high voltage bias conditions that does not lead to the formation of a corrosive by-product.